like hemiits asked,what is your timing curve and and like Cab said to much fuel at the hit will make it lazy especially if your timing is coming in slow

my old combo with a solid cam and 4000 converter would 60 in the 1.4s at 3700lbs. a 315 drag radial would be faster

I use to shift my standard port solid cam combo at 5800 and it ran 6.70s a lot heavier than you. your converter is fine. ports are to small